An Introduction to the Nervous System Organization and nerve cells

What is the nervous system? A network of specialized cells throughout your body. Carry electrochemical messages from one part of the body to another. Interacts with the endocrine system to maintain homeostasis. Nervous system works much faster than the endocrine system (electrochemical messages relayed by the brain versus chemical messages carried in the blood.

Divisions of the Nervous System Central Nervous System (CNS): consists of the brain and spinal cord. CNS is the control center for the body, actions (and messages) must pass through the CNS before being performed. Peripheral Nervous System (PNS): all other parts of the nervous system. Relays info between the CNS and other parts of the body.

Divisions of the Nervous System The PNS can be divided further into the somatic nervous system and the autonomic nervous system. The somatic nervous system controls voluntary movements of the body involving the skeletal muscles, bones and skin. It includes motor and sensory neurons. The autonomic nervous system is responsible for involuntary actions of the body and contains special motor nerves that control the internal organs of the body. Includes two divisions, sympathetic and parasympathetic.

Nerve Cells Two types of nerve cells, neurons and glial cells (aka neuroglia cells). Neurons are communication cells and the functional units of the nervous system. Neuroglia cells are non-conducting cells that support the nervous system. There are two different types of neuroglia; Schwann cells in the PNS and oligodendrocytes in the CNS.

Neuroglia or Glial cells Glia is a Greek word that means glue. Glial cells support and protect neurons, provide them with nutrients and oxygen, and provide insulation between neurons. Glial cells are capable of dividing via mitosis. Oligodendrocytes - Produce myelin sheath around nerve fibers in the central nervous system Schwann cells - Form myelin sheath in the peripheral nervous system What do you call a group of brains who form a singing group at school?

Gliomas Gliomas are tumors that develop in the brain involving the glial cells. Most cases of malignant brain tumors are gliomas.

Neurons Neurons are the oldest and longest cells in the human body. Neurons cannot divide via mitosis but current research suggests that adults can produce new neurons in their brains from neural stem cells.

Anatomy of a Neuron Cell body: Contains the nucleus, rough ER and other organelles. Responsible for the maintenance and daily activities of the cell Axon: a very long and thin extension of cytoplasm from the cell body. Carries impulses away from the cell body. Dendrites: much smaller cytoplasm extensions which carry impulses to the cell body (receive information)

Anatomy of a Neuron Myelin Sheath: a type of insulation that is wrapped around the axons of neurons. Helps reduce signal loss. Schwann Cells: produce the myelin sheath. A created by specialized glial cells wrapping themselves around the axon. Nodes of Ranvier: gaps between myelin sheath where the axon is “naked”.

Anatomy Neurilemma: a very thin membrane that can be found surrounding the axons of neurons in the PNS. Helps the neurons to regenerate after trauma. Neurons that lack a neurilemma and myelin sheath (grey matter of the brain) do not regenerate, which means trauma to those neurons is permanent.

Myelin Sheath on Neurons Functions: Saves the neuron energy Helps neuron maintain itself Speeds up the transmission of impulses Helps damaged or severed axons regenerate In multiple sclerosis the sheaths of myelinated neurons of the CNS become scarred. (pg 414)

Sensory Neurons Aka afferent neurons Pick up and relay information from the external environment to the CNS Found in clusters, known as ganglia, outside of the CNS. Ears, eyes, skin, nose, tongue, etc.

Five Types of Sensory Neurons Photoreceptors: sensory receptors in the eye that respond to light. Chemoreceptors: sensory receptors in your nose and on your tongue that respond to or are sensitive to chemicals. Thermoreceptors: sensory receptors in your skin and hypothalamus that respond to warm or cold temperatures.

Five Types of Sensory Neurons Mechanoreceptors – sensory receptors that respond to mechanical energy. These receptors detect touch, pressure, vibration, limb position, muscle length, and tension Pain receptors – sensory receptors that respond to tissue injury and excessive pressure.

Motor Neurons Aka efferent neurons. Carry signals from the CNS to effectors. Effectors: muscles, organs, glands. Produce responses such as movement and release of hormones.

Interneurons Neurons between neurons. Located mostly in the spinal cord and brain. (grey matter) Link sensory and motor neurons to each other Interpret the messages picked up by sensory neurons

Reflexes Reflex arc: a circuit through the spinal cord consisting of a sensory neuron, interneuron and motor neuron. Reflex actions are not carried to the brain, instead they are interpreted in the spinal cord. Reflexes help prevent major injury by reducing the amount of time it takes for the reaction to happen after the sensory input.

Reflex Arc Review Five basic components of the reflex arc Receptor Sensory neuron Interneuron in spinal cord Motor neuron Effector